1. Field of the Invention
The present invention relates to a start control apparatus for an internal combustion engine, for controlling fuel injection at a cold start of the internal combustion engine.
2. Description of the Related Art
For starting an internal combustion engine (hereinafter, also referred to simply as an “engine”) at low temperature, it is difficult to ensure stable starting performance because a fuel is unlikely to be volatilized for a fuel temperature and an atmospheric temperature which are both low. Moreover, since a large amount of fuel must be injected at the engine start, an exhaust gas problem disadvantageously becomes more serious.
Recently, with growing concern about air pollution, changes in oil situation, and the like, alcohol has attracted attention as an alternative fuel for gasoline. For example, a flexible fuel vehicle (FFV) using a blend fuel of ethanol and gasoline (0% to 100% ethanol) has been put into practical use. However, in general, alcohol is less volatile at low temperature than gasoline. Therefore, for the engine start at low temperature, the deterioration of cold startability and the deterioration of the amount and quality of the exhaust gas when a fuel having a high alcohol concentration such as ethanol 100% (E100) is used become particularly problematical.
For improving the cold startability and improving the amount and quality of the exhaust gas, the following method is known. According to the method, a fuel is warmed by a heater provided inside an injector or to a fuel pipe or an intake port to promote the volatilization of the fuel. Thereafter, the fuel is used for combustion in the engine.
Moreover, for example, Japanese Patent Application Laid-open No. Hei 3-070852 (hereinafter, referred to as Patent Document 1) discloses a starter auxiliary device of an alcohol engine, which includes start possibility judging unit, necessary calorific value calculating unit, and start control unit. The start possibility judging unit judges based on an alcohol concentration of a fuel and an engine temperature whether or not the engine can be started. The necessary calorific value calculating unit calculates a necessary calorific value of heating unit for promoting the vaporization of the fuel to allow the engine to be started based on the alcohol concentration and the engine temperature when the start possibility judging unit judges that the engine cannot be started. The start control unit compares the necessary calorific value calculated by the necessary calorific value calculating unit and a predetermined reference value, and energizes the heating unit for a predetermined period of time when the necessary calorific value is larger than the reference value to then drive a starter motor.
Further, Japanese Patent Application Laid-open No. Hei 5-086917 (hereinafter, referred to as Patent Document 2) discloses a start control method of an engine for an FFV. The disclosed start control method includes the steps of: obtaining a start time increment coefficient from an engine temperature at the engine start and a concentration of alcohol in a fuel; obtaining an intake air temperature correction coefficient from a difference between the engine temperature and an intake air temperature, and the alcohol concentration; obtaining a fuel temperature correction coefficient from a difference between the engine temperature and a fuel temperature, and the alcohol concentration; and comparing a start possibility judgment value with a value obtained by multiplying the start time increment coefficient, the intake air temperature correction coefficient, and the fuel temperature correction coefficient, and starting energizing heating unit provided in a fuel injection direction of an injector when the value obtained by the multiplication is larger than the start possibility judgment value.
According to the conventional methods, however, the start possibility judgment or the necessity of heating, and further, for example, the fuel injection amount is obtained based on states such as a cooling water temperature and the fuel temperature before the fuel is heated. Therefore, the judgment of the necessity of heating or the setting of the fuel injection amount, which is suitable for a fuel volatility varying depending on a fuel heating temperature, is not performed. Accordingly, an overrich condition is caused by the excessive vaporization of the fuel to deteriorate a combustion state, or an overlean condition is caused by the insufficient vaporization of the fuel to deteriorate the combustion. As a result, the startability is adversely deteriorated.
Moreover, although a fuel injection amount is reduced while the fuel is being heated in the above-mentioned conventional methods, the amount of reduction is fixed, and therefore the fuel injection amount suitable for the fuel volatility varying depending on the fuel heating temperature is not set. As a result, the overrich or overlean condition is caused to deteriorate the combustion, which in turn adversely deteriorates the startability.
Further, at engine restart after the injection of a heated fuel but with an unsuccessful engine start, the volatile state of the fuel in an intake port and a cylinder is ameliorated. Therefore, if the same amount of the heated fuel as that for the first engine start is injected for the engine restart, the vaporization of the fuel becomes excessive to put the engine into the overrich condition. As a result, the startability is adversely deteriorated.